An abandoned, 20,000-pound Chinese space station is about to take a nosedive through the Earth’s atmosphere, pulverize into a thousand little pieces, and strike the planet somewhere between the latitudes of 43° North and 43° South—the horizontal swath of land between, say, Syracuse, New York and Trelew, Argentina.
While the space station, called Tiangong-1, won’t remain intact upon re-entry, its parts could scatter within about 400 miles of its ground track—the path that the spacecraft takes as it projectiles through the sky at (currently) a speed of 15,000 miles per hour.
Sounds scary. Should you plan on spending the day underground? Or wear a helmet and keep your eyes tilted skyward, ready to dodge pieces of flying debris?
It turns out there’s no need to worry.
Objects about the size of Tiangong-1 enter the Earth’s atmosphere a couple of times per year, says Andrew Abraham, a member of the Mission Analysis and Operations Department of The Aerospace Corporation, a nonprofit that has been monitoring this situation ever since China disabled communications with the space station in December of 2015. So Tiangong-1’s fall to Earth isn’t a major deal. Plus, it’s lightweight compared to several other space stations that have re-entered in the past. “It wouldn’t even make the top 15 or 16,” Abraham said. “It’s big, but not remarkably huge.”
To date, only one person has ever reported being hit by space debris. In 1997, a shard of a Delta II rocket smacked Lottie Williams of Tulsa, Oklahoma on the shoulder. “It actually bounced off of her and didn’t harm her,” Abraham said.
Still uneasy? Scientists estimate that the probability of being hit by a piece of space debris from Tiangong-1 is approximately 10 million times smaller than the chance of being hit by lightning once over the course of one year. If a piece of debris does happen to hit your car, China is technically responsible for the damage.
Far from posing a threat to our bodies or our livelihoods (only about 10—40% of the original mass of Tiangong-1 will make it down to the surface of the Earth), an innocuous object in low-Earth orbit (LEO) like this one can instruct us on the intricate trajectories of other, more dangerous objects that might cross our path and threaten national security.
Vishnu Reddy, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory, is using Tiangong-1 as an opportunity to pull together an optical sensor package that documents the spacecraft’s progress. This is different from pricier ground-based radar systems. Radar systems must be manned and operated, whereas optical sensors can run without human assistance.
“We decided to build something that could be deployed en masse,” Reddy said. “Our hope is that we would have a tracking system like this on every fire station in the U.S.”
Reddy’s work is part of a larger effort to improve our management of orbital space. LEOs are much trickier to predict than geostationary orbits (communication satellites, for example, occupy these types of orbits) because objects in LEO are moving much faster. Tiangong-1, specifically, orbits the Earth every 90 minutes.
A few other factors influence Tiangong’s position at any given moment. First, the drag from the atmosphere changes over time, as it is dependent on the density of the upper atmosphere, “which can change by an order of magnitude on very short timescales, like a day or two,” Abraham said. “Also, if there’s an unexpected solar event, [the space station] would re-enter a little earlier.” The second factor is the orientation, or attitude, of the space station relative to the direction it’s moving. Add to that the complexities of a tumbling spacecraft (if it’s not moving at a constant orientation), and you have a complicated code that scientists are only just figuring out how to crack.
Even if the motions of objects in LEO are loaded with uncertainty (a calculation made about one day in advance of impact has an accuracy of plus or minus 20%,) the research that scientists like Abraham and Reddy are doing is propelling us forward. You can follow the Tiangong’s fluctuating path here, and read more about the impending crash here.
Abraham says to watch for the debris in the next few days, as re-entry will be quite the spectacle (report a sighting on Aerospace’s site here).